In preparation for performance of an NIH funded study of pulmonary perfusion in patients with the Adult Respiratory Distress Syndrome and the consequences of changing that pattern with a cyclooxygenase inhibitor (Lung Perfusion by Positron Emission Tomography) it is necessary to determine the lowest dose of the inhibitor (ketorolac) that inhibits thromboxane and prostacyclin production. Therefore, we plan to test reduced doses (20mg i.v. followed 6 hours later by 10mg i.v.) in five normal subjects with blood and urine measurements of TxB2, 6-keto P6F,alpha and their 2,3 dinor metabolites.